Airplane with two superposed wings

ABSTRACT

This invention relates to an improvement in an airplane having two superposedly-arranged upper and lower sweptback wings which together form a closed frame, with reference to a front view thereof, the improvement comprising a rhombic shape of the frame with the upper wing having a negative V-position and the lower wing having a positive V-position, both of the wings being rearwardly sweptback, and the upper wing being more markedly sweptback than the lower wing, and at least the leading edge of the upper wing being positioned forward of the lower wing.

The present invention relates to airplanes with twosuperposedly-arranged sweptback wings which together constitute a closedframe in a front view thereof.

Such wing configurations are based on the fact that, in the case of afinite wing moved through the air, there is effective, in addition tothe frictional resistance, an induced drag which is proportional to thesquare of the lift and inversely proportional to the geometric extensionof the wing in the direction of its span (in the direction of they-axis) and height (in the direction of the z-axis). Theseinterrelations were first dealt with theoretically by Ludwig Prandtl andMax Munk.

In the mathematical model representation used as a basis in thisconnection, the wing system is composed of lifting or supportingvortices with constantly changing circulation. Formed adjacent theretoare follower wakes or trailing vortices whose intensity of circulationcorresponds to the change of the wing circulation, and which extend toinfinity substantially in the current direction (in the direction of thex-axis). It is assumed in this connection that the form or shape of thevortex wake or trailing vortex and its circulatory distribution will notchange so that cross-sections through the vortex wake or trailing vortexat a right angle to the airflow direction always adopt the form or shapeof the wing or wing system about which the air flows, in a front view inthe direction of the x-axis. The position of the wings or wing partswith reference to the x-direction does not enter into this theory. Theinduced drag is accordingly dependent only upon the form or shape of thecross-section through the vortex wake or trailing vortex far behind thewing.

In the theoretical investigations of Prandtl et al and others, a numberof cross-sectional wing shapes, and thus of wing system shapes of equalspan and equal lift have been compared with each other. Indicatedtherein are the proportions or ratios of the induced drag of anon-planar wing system with respect to that of a planar elliptical wing.It was found that this resistance ratio K represents a code orcoefficient specific for a specific cross-sectional form or shape. Thus,for example a wing arrangement in biplane construction with a distanceratio of 0.5, based upon the distance of the wings in the direction ofthe z-axis, compared with a monoplane having a distance ratio of 0, hasan induced drag approximately 38% lower with the same span and the sameaerodynamic lift. Under the same premises, a wing with end plates havingthe same height as the distance of the wings of the biplane arrangementhas 47% less; an annular wing and a biplane arrangement with end plates(box wings) with a height ratio of 0.5 has only half the induced drag ascompared with the monoplane or single wing construction.

The aforementioned wing system in biplane construction has been knownsince the beginnings of flight. The advantage of this constructionresides, in addition to the low induced drag, in the low wing weightattainable therewith. Because of the necessary reinforcements of thewings, the undesirable resistance, however, is relatively high, and as aconsequence thereof, the use of this wing construction is considerablyrestricted.

While the construction with only one wing and end plates mounted thereonhas a very low induced drag, as has been mentioned hereinbefore, it doeshave a high specific wing weight. The results from the relativelyuniform circulatory distribution over the wing span which produces ahigh root bending moment.

In the known wing configuration in box form or shape, the straight wingsare provided in a staggered manner with respect to the incident airflowfrom the front, and specifically in such a manner that the lower wing,with reference to the oncoming airflow is positioned rearwardly withrespect to the upper wing. The wings are therein connected with eachother at their ends by end plates. The end plates have an inclinedposition in the direction of the x-axis corresponding to the staggeredarrangement of the wings. While this type of wing arrangement has arelatively low induced drag, here again there arise high root bendingmoments at the pivotal points of the wings at the air-plane fuselage.This requires at the wing root a corresponding wing thickness withadverse effects relative to the weight and also at supersonic flow.

Another known wing construction or arrangement has two wings, whereinthe forward one has a trailing sweep with negative V-position, and thesecond one has a forward sweep with positive V-position. The two wingsterminate in a common wing tip.

Known moreover is a wing configuration which has a rearwardly sweptbackupper wing without V-position, and a lower forwardly sweptback wing withpositive V-position, wherein the wings extend at the outer edges thereofinto spindle-shaped bodies.

Additionally known in the art is a wing configuration which isbox-shaped in a front view and in which a lower rearwardly sweptbackwing is interconnected with an upper forwardly sweptback wing by way ofsweptback end plates.

It is the object of the present invention to provide an airplane of highmaneuverability and adaptability with simultaneous provision for highflying speeds by means of a special wing construction having a high liftcoefficient with small resistance, both in supersonic and subsonicranges, as well as having low weight.

In such an airplane which is intended to have high maneuverability, anumber of requirements must be met which bear close relationship witheach other. Thus, the wing construction must produce as low a resistanceas possible both at subsonic and at supersonic speeds. Furthermore, ahigh lift coefficient must be attainable, and lastly, the aforementionedrequirements must be attainable under the condition of as low a weightas possible.

From the stipulated requirements result, however, a number of problemswhich, in the known wing configurations, cannot, or can be only partly,considered as having been solved. When, for example, an airplane isconstructed with a wing having a large aspect ratio or span, only therequirements of low resistance at subsonic speed and a high liftcoefficient are attainable. In order that one be able to fulfill therequirement of a structure having the lowest possible weight, relativelythick wing profiles are needed for as great as possible a height of thewing spars. Such a construction, in turn, contradicts, however, therequirement, also to be considered, of as low as possible a resistanceat supersonic speeds. For supersonic flow, thin wing profiles areemployed inasmuch, as is well known, the wave resistance or dragincreases to the square with the profile thickness. The load factorarising in airplanes with a high maneuverability during flying maneuversforces one to use relatively compact wings, i.e. wings having a smallaspect ratio. With this construction, however, the requirement for thelowest possible resistance and greatest possible lift coefficient is notattainable, as already has been indicated hereinabove.

In order to arrive at better solutions, or at least compromises withrespect to the requirements stipulated hereinabove, it has become knownin the art to produce additional vortices, for example by means ofstrake wings, or to provide auxiliary wings. The additional vorticesalso may be stabilized by means of gas jets, as is generally known.Another known measure in this connection is the provision of leading andtrailing edge flaps, or the pivoting of the entire wing. These measures,however, significantly increase the weight due to the lift necessary forthe pivoting of the wings and/or flaps, and also increase the requiredcosts. Yet, with the wing constructions or configurations known to date,the disadvantages indicated cannot be eliminated without compromisesolutions.

The object sought to be obtained according to the present invention isattained by virtue of the fact that the frame arrangement of the wingshas a rhombic form or shape with an upper wing having a negativeV-position, and a lower wing having a positive V-position, that bothwings are rearwardly sweptback, that the upper wing has a greatersweepback than the lower wing, and that the upper wing is positionedahead of the lower wing at least with its front edge, with reference tothe airflow from the front.

With such a wing construction and arrangement it is possible to realizean airplane having an extremely high maneuverability. The induced dragis low both in the subsonic and also in the supersonic ranges withrespect to the known wing constructions, with a simultaneouslyrelatively low weight. While, in the box wing, the aerodynamic forces atthe wing connection are transmitted, as in the individual or singlewing, also as transverse force and as root bending moment, the rootbending moment is eliminated in the wing system provided by the presentinvention. What does arise are only transverse and longitudinal forcesso that at the inner wing part (the wing part in proximity to thefuselage) and the wing connection structure of the fuselage, aconsiderable amount of weight is saved. With the determined structuralweight of the airplane it is possible, according to the presentinvention, that the wing system be imparted a greater span and that thusthe induced drag be reduced. As a result of the fact that, in theinventive wing construction, the root bending moment is eliminated, itis possible that the individual or single wings be hingedly connected atthe fuselage. In this manner it is possible that in the area of theinner wing, i.e. the part of the wing positioned in proximity to thefuselage, a profile thickness of 1 to 2% of the profile depth isrealized, whereby the wave resistance or drag is there greatly reduced.The mutual wing support allows for a relatively great span and area ofthe wings, and, on the basis of the mutual wing interference, a highmaximal lift is achieved without movable flaps. This too signifies afurther reduction of the weight of the aircraft. Furthermore, a highlift coefficient thereby may be achieved both in the subsonic and in thesupersonic ranges.

It is further proposed, according to another embodiment of the presentinvention, that, with approximately half the value of half the span,both wings have a vertical height distance of approximately one third ofthe depth of one of the wings. This particular construction of the wingsystem results, with the corresponding adjustment (setting angle) of thetwo wings with respect to each other in a two-dimensional flow, in abiplane arrangement by means of which an improved glide ratio and a highmaximal lift are achieved as compared to individual or single wings.

For the further embodiment of the present invention it is also proposedthat the upper wing is more markedly sweptback than the lower wing andincludes approximately a negative V-position within a range of 6° to10°, and the lower wing includes a positive V-position within a range ofapproximately 6° to 10°.

Furthermore, a specific embodiment of the inventive wing system consistsin that at least one of the two wings has within the area of thefuselage markedly sweptback front edges drawn or pulled forward in knownmanner. Strake wings produce the free forward edge vortices known fromdelta wings which contribute to a further increase of the lift.

According to yet another embodiment of the present invention, it isprovided that the wings are interconnected within the area of the outeredges thereof. Moreover, it is proposed by the present invention thatboth wings adjoin a common wing tip, and that the wings structurallyadjoin each with the outer edge thereof a common disc-shaped end profilepart extending at a right angle to the wing span. Thus formed is astructurally rigid triangular connection. As compared to the single wingor monoplane and the box wing, the root bending moment is advantageouslyeliminated, as already has been mentioned hereinbefore. Only transverseand longitudinal forces arise so that the connecting wing structure maybe dimensioned correspondingly lighter. With the predeterminedstructural weight, a further increase of the wing span thus may berealized. Also achieved with the inventive construction, in addition tothe features set forth above, is a significant improvement of themaximal lift and of the glide ratio.

A further essential feature of the present invention moreover resides inthat the wings display directly in the area of the outer edges a heightdistance with respect to each other which is smaller than one third ofthe wing depth.

The inventive wing system is not limited to the use in airplanes of thetype mentioned herein. Rather, also the wings of transonic transportplanes may be constructed in the manner set forth herein. Also the wingsof hydrofoils may be constructed as proposed by the present invention.

Embodiments according to the present invention and a comparison ofvarious wing configurations are illustrated in the accompanyingdrawings, wherein

FIG. 1 is a side view of an airplane with the inventive wing system;

FIG. 2 is a front view of the wing system according to FIG. 1;

FIG. 3 is a top plan view of the wing system according to FIG. 1;

FIG. 4 is a perspective view of the inventive wing arrangement orconstruction;

FIG. 5 is a schematic view of the flow conditions or ratios at the wingsystem, in perspective;

FIGS. 5a through 5c schematically illustrate, in a section from FIG. 5,embodiments of the wing tips, and

FIGS. 6a through 6c illustrate the comparison of known wingconstructions with the inventive wing system in a graph for purposes ofcomparing the wing distances in the direction of the vertical airplaneaxis and the span.

The airplane illustrated in FIGS. 1 through 5 of the drawings has afuselage 2 with the nose 3, the fuselage central part 4, and the tailpart 5. Arranged in the conventional manner at the tail part 5 is thetail unit or assembly which has here a pendulum horizontal stabilizer 11and a rudder assembly fin 13 with a rudder surface 14. The specificarrangement of the horizontal stabilizer 11 at the airplane fuselage 2will be further described hereinbelow.

Hingedly connected to the airplane fuselage 2 are an upper rearwardlysweptback wing 20 and a lower equally rearwardly sweptback second wing20'. The upper wing 20 has a negative V-position while the lower wing20' has a positive V-position. The upper wing 20 is secured to thefuselage 2 in the form of a high-wing monoplane arrangement and theother wing 20' in the form of a low-wing monoplane arrangement. Bothwings 20 and 20' extend toward their outer edges 25 and 25' with atrapezoidally-decreasing wing depth T. In the front view, i.e. seen inthe direction of the x-axis (the longitudinal air-plane axis), the wings20 and 20' circumscribe a closed frame which has the form or shape of arhombus or of a parallelogram.

On both sides of the airplane fuselage 2 the two wings 20 and 20' abutwith their outer edges 25 and 25' against the end profile parts 23 andare structurally rigidly connected therewith. The end profile parts 23,in addition to being provided for structural purposes, also serve forpreventing the lateral flow at the wings in the direction of the outerwing edges 25 and 25', and thus contribute to a lift increase. The unionbetween the fuselage 2 and the wings 20 and 20' does not require a rigidconnection. The forward or leading edges of the two wings 20 and 20' aredefined with reference numeral 21, and 21', and the rear or trailingedges thereof are identified with reference numerals 22, and 22'. In theembodiment shown, viewed in a top plan view, the forward or leading edge21' of the lower wing 20' is positioned under the rear or trailing edge22 of the upper wing 20. In the area or range of half the span of thewing halves of the upper and lower wing 20 and 20', the distance or gapS (FIG. 2) between the two wings, with reference to the verticalairplane axis z amounts to approximately one third of the depth T of thewing at this point. This results - with the corresponding adjustment orsetting of both wings 20 and 20' with respect to each other in atwo-dimensional flow - in an optimal biplane arrangement.

Δ α identifies the setting angle of the two wings 20 and 20' withrespect to each other. In conjunction with the vertical interval orseparation h of the wings 20 and 20', this adjustment or setting hasspecial importance, namely with respect to an improved glide ratio and ahigh maximal lift.

Both in the case of the upper and of the lower wing 20 and 20', theforward or leading edges 21 and 21' are markedly sweptback and drawnforwardly in the area of the fuselage 2 so that so-called strakes 30 and30' are produced. These strakes produce the free forward or leading edgevortices W (FIG. 5) which are known from delta wings and whichcontribute to an additional increase of the lift at the wing. Furtheridentified with reference numeral 6 is the position of the propulsionunit of the airplane. In the embodiment shown of the wing system, theair intake 7 of the propulsion unit 6 is advantageously positionedbetween the wings 20 and 20' and below the strake 30 of the upper wing20. This position is favorable also at large angles of incidence or wingsettings of the wing system against the flow.

As is further apparent from FIG. 3 and FIGS. 5a through 5c, a number ofpossibilities of construction are conceivable for the wings in the areaor range of the outer wing edges 25 and 25'. FIG. 3 shows an embodimentin which the two wings 20 and 20' join an end profile part 23 and changeover into a common wing tip 26 and 26'. In this case a gap S has beenleft at the connecting point of the two wings 20 and 20' (see also FIG.5b).

By contrast, in the embodiment according to FIG. 5a, the provision wasso made that the two wings 20 and 20' are rigidly connected with the endprofile parts 23, and also in this case a gap S has been left at theconnecting point of the wings 20 and 20' with the end profile parts 23.In both the embodiments according to FIGS. 3 and 5b, the wings 20 and20' are connected over the wing tips 26 and 26' and/or the end profileparts 23 to form a rigid triangular union or formation. By means of thewing tips 26 and 26', an increased wing aspect ratio is moreoverachieved aerodynamically.

In the embodiment according to FIG. 5c, the upper wing 20 has in thearea of its outer edges 25 a connection with the lower wing 20' and wingtips 32a and 32a' with a positive V-position, and the lower wing 20' hasa connection with wing tips 32b and 32b' with a negative V-position.Here again an air gap S has been left at the connecting point (25 and25') between the upper and the lower wing 20 and 20'.

For the missing control flaps at the wings 20 and 20', the horizontaltail unit is so constructed that it assumes the rolling and altitudecontrol, as is generally known.

As is apparent from FIG. 6, three wing systems are therein compared withthe premise of equal aerodynamic performance.

In an airplane configuration actually made, the induced drag is ofdirect interest, and specifically for determined values of lift A andflying speed U∞. For the induced drag Wi, ##EQU1## has validity, as hasbeen stated already. Therein Wi is the induced drag, K the induced dragratio, A the lift, U the relative wind velocity, and b the wing span, aswell as ρ the air density. It is obvious therefore that the induced dragratio, in the aforestated equation, comes in directly, but the span tothe square. If two different wing systems are to have the same lift atthe same flying speed and at the same induced drag, the followingequation may be derived therefrom: ##EQU2## wherein K₁ and K₂ representthe induced drag ratio of two wing systems each being compared with eachother. According to this equation, the systems shown in FIG. 6 arecompared with each other. What is treated here in these wings are abox-type wing with the altitude ratio for example of 0.3 with the wings20_(K) and 20_(K) ', and the vertical wing part 20_(V), a rhombic wingaccording to the present invention, and an equivalent single wing,wherein the wing has been identified with reference symbol 20_(E).

The reference letter h identifies the distance between two wings in thedirection of the z-axis of the wing system. While it is true that thespan of the rhombic wing is by 27.5% larger than in the box-type wingwith the same performance, the circumcirculated surface which stronglyenters into the weight of the wing (here the developed length 1 of thecross section) is smaller by about 1%. While in the box-type wing20_(K), 20_(K) ' the aerodynamic forces at the wing connection aretransmitted in the conventional manner as in the single wing astransverse force Q and as root bending moment M, the root bending momentis eliminated in the rhombic wing 20, 20'. Only transverse forces Q andlongitudinal forces L arise so that at the inner wing (at the inner partof the wing) and at the wing connecting structure at the fuselage,weight is saved. With determined structural weight, the rhombic wing 20,20' may be given a further increase of the span b than is apparent fromFIG. 6 which, according to the equation for the induced drag, means alower induced drag.

It will be obvious to those skilled in the art that many modificationsmay be made within the scope of the present invention without departingfrom the spirit thereof, and the invention includes all suchmodifications.

What is claimed is:
 1. In an airplane having two superposedly-arrangedupper and lower sweptback wings which together form a closed frame, withreference to a front view thereof,the improvement comprising that saidupper wing is connected with the airplane fuselage in the form of ahigh-wing monoplane, and said lower wing is connected in the form of alow-wing monoplane, said frame having a rhombic shape with said upperwing having a negative V-position and said lower wing having a positiveV-position, both of said wings being rearwardly sweptback, and saidupper wing being more markedly sweptback than said lower wing, saidwings being staggered in the direction of the wing depth and air flowsuch that the trailing edge of the upper wing is positionedapproximately over the leading edge of the lower wing, plate-like meansextending parallel to the vertical longitudinal central plane of theaircraft and connecting the outer parts of the upper and lower wings ina vertically staggered manner, and wing tip means, extending the wingspan and common to both wings, associated with said upper and lowerwings.
 2. An airplane according to claim 1 in which said wing tip meansare outboard of said plate-like means.
 3. An airplane according to claim1 in which said plate-like means form end plates at the wings and extendbeyond at least one of said upper and lower wings.
 4. An airplaneaccording to claim 1 in which at least one of said wings has a moremarkedly sweptback leading edge portion than the remainder of said wing.